1. Field of the Invention
The present invention relates to a binary-coded image information producing apparatus used in black/white copiers, facsimiles, and other electronic products.
2. Description of the Related Art
Up to now, various methods and systems have been proposed by which binary-coded image information can be obtained from analog image information. In general, most of these binary coding methods/systems aim to more accurately represent an original image, by which a half tone image can be represented as a quasi-half tone image.
As the above-described quasi-half tone image producing method such a quasi-half tone image has been represented by obtaining a binary coded image, while varying a dot number within a predetermined area in response to a tone of an original image.
However, for some practical applications it is necessary that only a certain portion of interest contained in an original image must be duplicated as a sharp image. For instance, when the portion of interest photograph is only the black alpha-numeric characters included in it, difficulties arise in reproducing the characters well with such binary coding methods capable of representing a quasi-half tone image. That is, it is sometimes difficult to discriminatively represent these black-colored characters printed on the quasi-half tone image. The reasons are as follows. Since, as previously described, the dot quantity of the image is varied in accordance with the tone of the original image, there is no change in the dot quantities of both the characters and background portion in case that practically no difference exists in the tones between the characters and background.
Furthermore, a tone of an area around a contour of characters and a background thereof is represented based upon dot quantities of these contour and background so that the sharpness of the character contour is deteriorated. In such a case, a binary coding method capable of accurately and sharply reproducing the alpha-numeric characters contained in an original image is preferable to a binary coding method which is meant to be capable of correctly reproducing the entire original image.